Spinning optical scanners are the subject of such patents as disclosed in the applicant's U.S. Pat. No. 3,953,105 and involve a plurality of holograms recorded on a rotating surface. Recent advances have been directed toward the development of what may be called two-dimensional scanners. In such devices, the surface or object being scanned is being scanned laterally and longitudinally, and the two-dimensional name is apt. In such systems, high speed, high resolution and high reliability coupled with simplicity and low cost are factors investigators are seeking to supply. These image-producing systems use energy sources such as a laser in the visible, ultra-violet and infra-red range, millimeter and micro-waves as well as ultrasonics. While such sources may be used within the principles of this invention, the invention will be described with particular reference to the use of the laser beam in the visible region.
Because of its high intensity and capability of being focused to a small spot, the use of the laser beam in scanning is becoming increasingly important in high-speed interfacing of two-dimensional information with computational and communication systems. If laser scanning systems can be greatly reduced in cost and complexity, as, for example, in the manner described here, such systems might also be incorporated in high resolution display systems.
In prior art devices, multifaceted pyramidal mirrors are frequently used despite many problems involved. For example, conventional rotating mirror scanners can provide a one-dimensional scan in the direction of rotation. A complicated arrangement, however, is needed to provide two-dimensional scans. High precision is often required for these scanners and it is achieved and maintained entirely by mechanical means. For these reasons these scanner systems are not only very expensive, but are also unreliable and difficult to operate. They are also burdened by a number of manufacturing problems. For extreme high-speed operation, the mirror-surface deformation and air turbulence caused by the facet edges seriously affect the performance of such mirror scanners.
The use of holograms to replace mirrors as scanners has been suggested and demonstrated recently. Holographic scanners have essentially removed most of the manufacturing problems associated with mirror scanners. The difficulty for providing a high resolution, two-dimensional scan, however, remains unchanged.
Thus, it is an object of this invention to provide two-dimensional scanners at low cost and simple operation. Another aim is the provision of such a scanning system that is, in effect, a single scanning system that automatically provides two-dimensional scanning. A further purpose is to provide a system using a plurality of holograms and a laser beam. A still further objective is the affording to the public auxiliary equipment, such as a photodetector, to convert light signals to electrical signals for transmission to distant points. An additional aim is providing at a distant point a similar scanning system of this invention to function as a receiver with a modulator to act upon a photosensitive film at said distant point. These and other objects will appear by reference to the discussion below and to the drawings which are given for illustrative purposes only and are not limitative of the principles of this invention.